Modern Vespa

Hi all

Looking for an outer engine casing for SS180. In case you have one lying around and could do with selling it. Anywhere in the world is fine.

Many thanks!

That's a tough one to find.
Good luck.

True and thanks.

Is it possible to use a GS160 engine case mated to an SS180 engine case? I need the outer case and can't find an SS180 unit. Would the two halves match up? Would it need boring?

I have read that the engine cases are the same but it can't be as simple as that.

Thanks all!

Are you talking about using one case half of a GS160 mated to one case half of an SS180?

Or, are you asking about using an entire GS160 engine with a SS180 top end?

*I think* the latter is possible if it were to be a Mk2 GS160. The former would be inadvisable even if possible.

As SS180's are more common in Europe I think you could find a reliable shop in the UK (Swiss Tony's, Disco Dez, etc), or one in Italy, and have them be on the hunt for you?

You could also post in the FB SS180 group but be wary of scammers and dubious replies.

https://www.facebook.com/groups/356147511111516

I would also reach out to these folks

https://www.maskesvespaparts.com/

They have a ton of stuff in their warehouse. Might be worth asking.

Yep.

It would probably "work" but that would not be ideal. The bearings are the same between them and the cylinder mouth should be the same.

I know people have used unmatched cases and everything was "fine" but the factory took the time to line-bore and number match cases for a reason. It's a much better engine in the end.

I would not do it.

I have a damaged case on an otherwise great bike. It won't start with compression around 75psi. The solution is to find an SS180 outer case to replace the damaged item. I was wondering if I could use a GS160 case instead.

I know it's not ideal but it could be a solution.

I can't find an SS180 engine or case but I can locate GS160 parts that would work.

Would the two halves mate together OK?

Strongly recommend you keep looking

So even though some people say the SS180 and GS160 engine cases are the same, they are actually not? Or they are?

Does anybody know? I expect bearings and anciliaires to be different but the cases look the same.

I am trying to find Vespa part numbers to confirm.

Thanks all!

So what are you suggesting is damaged? If the case is not holding pressure, is the rotary valve worn? If so Hot Rod Al is now back in business and can rebuild the rotary valve.

The outer case has missing metal where there has been some historic damage. I took it to a local engine rebuild company who said it couldn't be repaired but there is a possibility that gasket seal may work. I put it back together hoping it would work and create a good seal but still have the same low compression.

So now need a replacement outer case.

Got a picture of the damaged area?

https://www.facebook.com/groups/342844209095322/

Just listed.

Thanks - I may have a more local option (UK). No pics at the moment but will take one when the engine is apart again.

Just a quick question on compression before I take the engine apart again...

Piston rings are in very nice condition and there is no scoring or damage on the inside of the cylinder. I can test for leaks at the base of the cylinder with soapy water but I used a new gasket and the long bolts are tightened so I think it is unlikely I will see any leaks here. Anything else that is an obvious cause of low compression that I should be looking at?

Next time the engine comes apart will be to install a replacement outer case.

If you/or someone else have had the the cases open, the probability that you have a leak is near 100%. If you have not already done so, build a proper leak test rig and make sure you have proper seals all around.

Serious About Air Leaks

Thanks, that's very helpful, even without pics. I have a blood pressure testing kit and a compression tester. I need to make a block of rubber to block the carb intake. Sealing exhaust is straightforward.

Will do it...

When you check compression with a compression tester in the spark plug hole, you are only testing pressure above the rings. Anything below is not designed to hold say, 100psi. In fact when you test with your blood pressure unit, you should only go to something like 5psi ish.

Your 75psi is only telling you about the state of the rings and their seal to the bore.
Test again with a squirt of oil down the plug hole. That will temporarily seal the rings. If the compression comes up then you know the problem is there.

Thanks for this Ginch. Will do. If this figure is low is it right to suspect the rings are worn? I could easily replace with new and retest.

More with pix.

Pressure test question

The test after a squirt of oil will tell you. The bigger the difference between the before and after pressure, the more the rings will be worn.

Let's know how you get on.

Compression test with no oil 75. With oil about 85 - using thin multi purpose oil.

About five kicks gets it to its max.

Working on the air leak testing kit and will do that next.

Leak test part one...

Are you sure the damaged case side is causing your issues? And if it is, I'm thinking there must be a way to repair it. Maybe check around more when you get the engine torn down.

I've had cracks welded up and machined with success. I know that is not the same as patching in sections but I think that could be done. Finding the right people is key. That could solve your problem in the best possible way.

The cases look decent from your engine picture. I'm waiting to see pictures of it when its apart.

Not sure, hence all the questions and the testing. I don't want to take the engine apart again until I have narrowed down the issue.

Compression + leak testing then will figure out what to do.

At the moment I have a bike that has only run from cold for a few mins then refuses to restart. Have done seals, have re-done the case gasket with extra heavy material. Spark is lovely, fuel is good, everything else is tickedy boo. Need to narrow down exactly where the compression issue is.

I took the case half to a very experienced local engine builder. Not an easy repair but also may work as is. Followed his advice and put the engine together using threebond gasket.

How thin is thin multi purpose oil? The point is to make sure it seals, so it has to be thick enough to do that. Otherwise it's going to run past and not have much effect.

When you are doing a compression test, does your gauge have a schraeder valve installed? These small engine don't move a lot of air and you need to minimize the length of the hose to the gauge and have a schraeder valve installed in your test rig otherwise you can get questionable compression readings. Process: (1) Warm engine, if possible. (2) WOT. (3) 5-10 good kicks.

At 7.7:1 compression your SS180 should be seeing about 113 psi (7.7 x 14.7), if all is well.

Not seeing how having the throttle WOT makes any difference on a compression test.

The cylinder's open to the air at the exhaust.

I've always read that's the way to do it. I see your point though.

Combustion engines are designed to flow air in one direction. They are "air pumps".

If you close the air intake, you imped air flow. This will impact air compression.

Is this wrong?

"A very reputable engine builder" is definitely not a Vespa mechanic and pretty hard to lose compression through defects in the cases as this relies entirely on the piston/rings/cylinder/head relationship....

Thanks for all the back and forth. Have done a leak test and have very minor leaks in the gasket under the carb. Not sure how significant this is.

Pretty sure there are no other leaks.

So with an engine that seems not to leak but low compression at the spark plug end of the cylinder I think the rings may be the issue.

Is there a science to getting the right rings? I think it's a standard SS180 cylinder. Take off the head and measure the inside of the cylinder with calipers?

Thanks.

It's significant. Any little leak will make it impossible to jet and will get worse over time.

[/quote] Pretty sure there are no other leaks. [/quote]
That's good.

[/quote] So with an engine that seems not to leak but low compression at the spark plug end of the cylinder I think the rings may be the issue. [/quote]
Your engine does leak. Fix that. Engine needs to hold 6psi for at least 15mins with no air loss. Once you've got that settled then move on to the next problem.

75psi no oil. 115psi with gear oil.

Time for new rings?

Yeah, got it. How are these paper gaskets supposed to create that tight a seal though...

OK, think we are close. Repositioned the rubber block under the carb spacer. Very very slow leak. I don't want to take the engine apart if I don't have to so my thinking is to change the rings, see if have better compression and if the bike will start.

Have used a stethoscope and can't detect any air escaping from listening to the case. No soapy bubbles from the carb gasket or cylinder gasket.

Definitely pursue any leaks you may find but I think your main issue lies in the more common areas of fuel and ignition issues.

Starting but then dying and than not starting points in that direction IMO.

Carb and spark my seem fine but beware.

Recheck these - Check fuel flow from tank. Check to make sure the float is working as it should. Make sure the float is not sticking down and causing flooding or Vice Versa.

Check the magnets in the flywheel. Will they hold a 19mm spanner?

Check the points. They should be very clean and function with no slop. New points are best but they can be poor quality too. Check the plastic bushing etc. The points should open and close smoothly and be perfectly aligned. If not bend them until they "clap" together perfectly. This is critical.

Make sure the felt pad has some clean oil on it to lube the cam.

Check the points gap. I find slightly tighter gaps work best. .015 thou or slightly less.

Check the internal coils and wire leads. If they are old, replace them.

Get a P125 external coil. Most if not all SS repro "bakolite" coils are junk.

Make sure the plug, the cap and the wire are solid with no issues. I like the NGK nonresistor caps the best.